with a headmaster does it throttle the refrigerant at a specific rate to keep proper head pressure or is it open/closed
http://www.sporlan.com/SD-134.pdf Check this out it has the answer I think your looking for.
The HP valve throttles open on rise of inlet pressure.
So as the ambient air entering the condenser coil gets warmer, the valve opens more to allow more condenser flow, so then, as the ambient gets colder, the valve closes in order to flood the condenser.
This cold flooded liquid will now mix with the compressor discharge gas and maintain head pressure.
A lot of guys get this mixed up and let it confuse them. It use to me too when I was starting in the trade. The one thing I might be able to help with someone understanding is the way I was taught.
When you block a condenser with a peice of card board, what happens? The pressure rises, is that correct? Of course it would because now your not rejecting the heat correctly to the ambient. Pressure and temperature rise together.
Well in the case of a head master, what we do is, we stack refrigerant inside the condenser. We reduce the capacity of the condenser by filling it partially with condensed liquid refrigerant. What ever part of the condenser is filled with condensed liquid refrigerant, is now rendered useless to condense any vapor. So in reality were using the refrigerant itself to block part of the condenser from being active by filling it with the liquid. were in effect making the condenser smaller.
When we reduce the "effective condensing surface area" we now have less of a condenser, which causes the head pressure to Rise.
As it rises, the headmaster valve stands at the ready, to allow passage of refrigerant to the receiver at whatever pressure setting the headmaster is set for. A common setting for r22, Sporlan LAC4 is 180 PSI. So that means, as the condenser pressure rises to 180 and above, we allow more and more refrigerant to leave out of the condenser and to pass to receiver.
Now think of the receiver. If I got 180 PSI, little by little being fed to it to allow passage to the receiver, I better have a lower pressure in my receiver for the refrigerant to flow from the condenser to receiver. If the receiver pressure was the same as the condenser, I'd never be able to flow out to receiver once my head pressure reached the setting of the headmaster. Generally, 20 PSI difference. So the receiver should be in the 160 PSI range.
As the ambient drops, this valve will modulate more and more to a position that stacks more refrigerant into the condenser to more and more elevate the head pressure to the headmaster setting.
How exactly does the Headmaster flood the condenser? Does i slightly close off the outlet of the condenser and cause the refrigerant to back up into the condenser? Also what does the discharge line do?
where does refrigerant like to go? The Niorth Pole? haha j/k well sort of Refrigerant likes to go(migrate where it's coldest. as cold ambient air is forced over the condenser coil that was designed to operate in an enviroment with much higher ambient temperatures, where it's so cold the refrigerant condenses quicker, (and it is colder and the pressure is lower, look at P/T Chart)
so a system with a headmaster has to have more refrigerant in the system(than an equivalant regular non "winterized" system) to compensate for the volume inside the condenser where the refrigerant wil be when it's cold and be able to keep a liquid level in the reciever over the bottom of the dip tube
so for summer operation the temp is up and it takes more area for the refrigerant to condense so the condenser is mostly high pressure vapor and the reciever level is higher(still the same ount of refrigerant in the syseem so it's(liquid refrigerant) not in the condenser and the level in the reciever is higher. so along with the headmaster the sysem has to have enough space in the reciever to handle the amount of refrigerant in the summer
where these syseems need more refrigerant for winter operation you can calculate the amount of refrigerant by looking at the size of the condenser, instructions for that are on the sporlan and alco head pressure control bullitens. when you get a new low ambient ready self contained condensing unit there will be a sheet in with it tellling you the "condenser charge, basically for an example it would say something like after sight glass is full weighe in additional 5.5lbs of refrigerant (made up numbers)
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Your not reading the details close enough bro. The headmaster is regulating pressure based on the inlet pressure to it from the condenser. This means that, if a head master is set for 180 PSI, the headmaster will not allow refrigerant to pass by it from the condenser to the receiver. If it's being blocked from passing, then this is how it begins to stack and flood the condenser. The other passage in the valve, is also proportional and allows the receiver to be 20 PSI less, with discharge gas being fed to receiver by the valove throttling based on the outlet also.
Originally Posted by yotaman16
Ok i get how the head pressure is being raised by the condenser being partially blocked by the liquid refrigerant that is being stacked in it. The headmaster can close the flow from the condenser to the reciever off to flood and raise the pressure up to the setting when then the valve will modulate to keep the desired or set pressure.. Am i right there or did i still miss somthing.. ALso how does the high pressure gas from the discharge line keep the reciever at a 20 psi diffirential from the condenser?
when the headmaster detects low head pressure, it allows discharge gas to bypass the condensor and go straight to the receiver. this increases pressure in the receiver which does two things.
1. force liquid out of the receiver
2. the increased pressure in the receiver is now higher than the condensor. this causes the refrigerant to back up in the condensor untill the condensing pressure is once again higher than the receiver pressure at which point the normal flow resumes.
as long as the headmaster is applying discharge gas pressure to the receiver, the condensing pressure will be artificially increased. The amount of gas that bypasses the condensor is negligable. it is only enough to increase the pressure in the receiver to the desired condensing pressure. it does not mix with the liquid and flow to the metering device.
and on the coldest day you'll get to top off the charge
the headmaster on some liebert's is set at 150. On very cold days if the system charge is a bit low( say 1 or 2 lbs.), the headmaster setting prevents enough gas from going to the evap--showing like a 15 psi suction. if everything is everything and you add a little gas, all of a sudden the suction will pop up to normal. then you get to plan on finding a leak and reweighing the total charge--preferably when it's not -6*.
but the headmaster was not seeing the 150psi or whatever that particular valve setting is...
It's great to be alive and pumping oxygen!
what does 'flood the condensor' mean? i thought gas went to the condenser, or do you mean that it over condenses?